And We know fully well what they say (by way of objection) that this (Qur'ân) is (not revealed by God but it is) only what a human being instructs to him (- to Muhammad). But (strange it is) that the tongue of him to whom they (unjustly) allude (of making this insinuation) is foreign and wanting in clearness, whereas the language of this (Qur'ân) is chaste Arabic, plain and clear.